One very, successful form of apparatus of the abovementioned general type is that sold under the registered trade mark "WEEDBUG" and the subject of Australian Patent No. 589361. Apparatus according to that invention may take various forms, including a tractor-mounted machine ideally suited to the application of weed-killing chemicals up to and around tree trunks, even in windy conditions. Typically the machine uses ropewick application from rotating discs or rotors fitted to adjustable arms so that the disc or rotor speed controls the chemical flow. Each rotor or disc has a cover assembly to roll around trees on soft bump edges, protecting the bark from abrasion while the disc works under the cover assembly. Such a machine can be operated under low hanging trees, and it may employ a single applicator rotor if desired, but usually two or more will be incorporated in each such machine which can also be used effectively along fencelines, road or pond edges, and in open areas requiring weed control.
Reference to the said Australian patent specification No. 589361 will show that the rotor has means whereby it may be rotated about an axis disposed substantially vertically in use and having a bottom disc through which the wick means extend for operation therebeneath, there being in practice a plurality of equally spaced wicks passing sealably through apertures in the disc from an annular reservoir above the disc and rotatable therewith. FIGS. 1 and 3 of the drawings of the earlier patent specification show basic requirements for the reservoir, while FIG. 4 shows an annular structure using the disc itself as a lower part of the reservoir. The arrangement for the wicks as shown in FIG. 5 of the earlier patent specification has been found very satisfactory in relation to design details, but most other components can be varied considerably within the broad ideas disclosed therein.
While the machines of the aforedescribed types, such as those sold under the registered trade mark "WEEDBUG", have been found very effective in achieving their objects, we have found that the continuous and consistent or steady application or flow of liquid through the wicks can be hampered by the fact that the reservoir is sealed to atmosphere except at the apertures through which the wicks pass to beneath the rotor disc. It will be appreciated that the withdrawal of liquid from the reservoir causes the formation of vacuum conditions which are currently relieved only by drawing back of air to the reservoir through the wicks or their mountings. The provision of a vent normally presents difficulties because liquid could be expelled centrifugally therethrough most undesirably. Also its location must not only be at an elevated position above liquid level in normal use, but it must take into account the fact that the rotors when inoperative can be swung upwards on the machine with the axis of rotation becoming or approaching horizontal and facilitating spillage through the air vent.
Our present invention has been devised to overcome or ameliorate the difficulties currently experienced as abovementioned, and it has for its principal object the provision of vent means for the reservoir whereby the desired venting will be achieved but without the disadvantageous consequences of a normal venting system as aforestated. Other objects of the invention are to provide a novel venting arrangement which can be put into effect without substantially altering existing design features of the machines. A further object is to provide such improvements which will be of simple and inexpensive form, which may be quickly and easily fitted, and which will prove reliable and durable in use. Other objects and advantages of the invention will be clear from the subsequent descriptions.